Ring ovens



V R; HL POWLL RING OVENS A -il 15, 1969 Sheet' of 4 Fd A ril 15, 1966 R. H, POWELL RING OVENS April 15, 1969 v Sheet Filed April 13. 1966 April 15, 1969 R. H POWELL RING OVENS Filed A ri 13. 1966 Sheet April' 15,`1969 R. H. POWELL RING OVEN Sheet Filed April 13. 1966 United States Patent 01 ice 3,438,739 Patented Apr. 15, 1969 3,438,739 RING OVENS Robert H. Powell, Surrey, England, assignor to Shandon Scientific Company Limited, London, England, a British company Filed Apr. 13, 1966, Ser. No. 542,325 Claims priority, application Great Britain, Mar. 30, 1966, 14,029/ 66 Int, Cl. G01w 31/20 U.S. Cl. 23-253 7 Claims ABSTRACT OF THE DISCLOSURE This invention relates to ovens and, more specifically, i i

is concerned with ring ovens.

The ring oven is used to convert a micro Sample in the form of a spot of dilute solution of a substance to be analysed into a concentrated thin line which may be of circular shape. The line may then, for example, be cut C into a number of segments each of which contains the same proportions of the substances as the original sample so that a large number of comparative tests can be conducted on the same initial micro Sample.

The conventional ring oven comprises an annular block of aluminum containing an electrical resistance heating element through which the current can be varied to heat the aluminum ring to dilferent temperatures. In use, the aluminum block is arranged with its axis upright and a filter paper is clamped across its upper end by means of a clamping ring. The inside rim of the clamping ring is coextensive with the bore of the block. The oven is .provided with a pipette support for mounting a pipette above the filter paper so that its lower end is coaxial with the block axis.

The solution to be concentrated is spotted as a Sample on the centre of the filter paper directly beneath the lower end of the pipette. Solvent is then allowed to flow gently from the lower end of the pipette onto the centre ofthe spot so that the Sample is carried with the Solvent radially outwards through the filter paper. When the Solvent reaches the hot boundary formed at the inside edge of the block and clamping ring, evaporation takes place and, in consequence the substances in solution are carried no further. As a result all of the dissolved substances are carried radially outwards to the hot boundary which therefore contains the same proportions of substances as were present in the Sample. The thickness, i.e., the annular width, of the hot boundary where deposition of the substances occurs as a result of evaporation of the Solvent is extremely small so that the concentration of the sample therein is high.

When the sample has been transferred to the hot boundary the filter paper can be removed from the oven when dry and the ring formed by the sample can be cut into a large number of segments. It will therefore be appreciated that the ring oven technique enables the diffused Sample to be split into a large number of parts, each of which contains the substances in the Sample in the same proportions and in concentrated form.

In a variant of the ring oven technique, concentration of a Sample may be carried out by applying the Sample as a streak across a strip of filter paper and by washing it downwardly through the paper which is provided intermediate its ends with a narrow waist formed *by suitably cutting the paper. The lower end portion of the filter paper directly beneath the 'waist is held between two heated plates having their upper edges extending across the waisted portion of the filter paper so that the descending Solvent is evaporated from the filter paper in the narrowest portion of the waist. As a result, the substances in the Sample washed down by the Solvent are concentrated as they flow towards the 'waist and are deposited as a concentrated line at the place where evaporation of the Solvent occurs. By using this technique a Sample Streak may be concentrated into a line of short length and negligible thickness.

Although the ring oven techniques described above are elegant and simple, the cost of ring ovens has apparently prevented their general use. It will be appreciated that the block in which the heating element is mounted has to be specially shaped to accommodate the heating element and also the heating element has to be carefully insulated from the metal of the block. Additionally, the control equipment necessary for varying the current flow through the heating element and thus temperature of the block increases the cost of the ring oven so that it is not generally available at a cost which *would facilitate its wide use by schools and other teaching establishments.

An object of this invention is the provision of a ring o'ven capable of being cheaply manufactured.

A ring oven in accordance with the invention comprises a base, gas burner means on said base, chimney means resting on said base and surrounding said gas burner means, heat conducting well means mounted on said chimney means, said well means closing the upper end of said chimney means and extending downwardly therein to define therewith an annular passage, gas outlet means extending through said chimney means from said annular assage, an annular filter paper support surface at the upper end of said well means, annular clamping means for holding filter paper on said support surface to span said well means, the inside diameter of the clamping means being the same as the inside diameter of said support surface, means for locating said clamping means coaxially of said support surface, pipette support means and a pipette carried by said support means *with its lower end overlying the center of said annular support surface.

A ring oven in accordance with the invention has the advantage that it may be cheaply constructed as use is made of heat from a gas burner to provide the hot boundary at which evaporation of the solution takes place. Gas burners are invariably provided with taps for controlling the gas flow therethrough and as a result the shaping and insulation of the metal block of the ring oven and the expensive electrical control equipment which formerly resulted in the bulk of the cost of the ring oven are avoided. Thus the oven of the invention may be made for as little as one third of the 'cost of a Conventional electrically heated ring oven and is therefore more readily available to schools and other educational establishments Where it may be desired to teach and use ring-oven techniques.

In a modification of the invention insert pieces are provided which fit snugly inside the well and define between them an upwardly opening slot for the reception of the lower end of a strip of downwardly hanging filter paper. As a result of the snug fit of the insert pieces in the well the heat from the well wall is transmitted to the insert pieces so that the slot provided between their opposed faces is uniformly heated. By using the insert pieces the ring oven is readily adapted for use in concentrating a spot or Streak on a strip of filter paper or from a chromatogram. The filter paper or strip is simply cut with a waist and the waisted portion is placed immediately above the top of the slot formed between the inserts so that the lower portion of the strip beneath the waist enters the slot. Solvent can then be released slowly onto the upper end of the filter paper or strip so that it flows down through the filter paper and past the spot. The constituents of the spot are dissolved in the solvent and carried downwardly by it to the waisted portion of the strip where, as a result of the waist, concentration of the dissolved substances in the solvent occurs. When the solvent reaches the position where the strip enters the slot it evaporates and the dissolved substances are deposited along a thin line at the place where evaporation occurs.

The invention will now be described in more detail, by way of example, with reference to the accompanying drawings, in which:

FIGURE l is a perspective view of a ring oven;

FIGURE 2 shows the parts of the ring oven in exploded form;

FIGURE 3 is a Vertical, partly sectional view through FIGURE l taken on the line indicated by the arrows III-III in that figure;

FIGURE 4 is a perspective view, with parts broken away, of the ring oven shown in FIGURE l but modified to handle a filter paper strip'provided with a waisted portion; and

FIGURE 5 is an exploded view of parts of FIGURE 4.

The ring oven of FIGURE 1 comprises a metal base 1 supported on three feet 2 and having a short length of gas pipe 3 projecting from its rim and onto which a length of rubber tubing extending to a gas tap can be connected. Resting on the central portion of the base is an upright aluminum chimney 4 provided at its top end with a radial flange S. Beneath the flange are a number of circumferentially extending slots 6 which provide hot-gas outlets and extend through the chimney wall. Resting on the peripheral portion of the flange 5 is a cylindrical glass shield 7. Inwardly of the shield and also resting on the top of the chimney 4 is an aluminum clamping collar 8 which is placed on top of a filter paper disc 10 spotted at 11 and spanning across the annulus of the clamping collar 8.

Projecting upwards from the top of the chimney 4 is a short post 12 which, with a gripping piece 13 detachably mounted on the top of the post, provides a support for holding a pipette 14 in coaxial alignment with the centre of the circular portion of the filter paper exposed within the annulus of the collar 8. The edge of the clamping collar 8 is cut away to provide a rebate 19 which seats around the post 12. The collar 8 is also provided with a hole 9 displaced by 90 with respect to the post 12 and which registers with a hole (see FIGURE 2) in the top of the chimney adapted to receive a thermometer (not shown).

FIGURES 2 and 3 show internal details of the ring oven construction. From FIGURE 2 it will be seen that the lower end of the chimney 4 is provided with a number of radially extending openings 20 of part cylindrical shape. The lower portion of the chimney closely surrounds a circular hub 21 projecting upwardly from the base and in the centre of which is set an upwardly pointing burner nozzle 22. The rim of the hub 21 is flared outwardly towards its upper edge 23 and the flared portion is provided with three dished depressions 24 allowing air entering the bottom openings 20 in the chimney to circulate upwardly past the flared rim of the flange and into a cylindrical combustion chamber 25 formed around the burner in the lower end of the chimney as shown in FIGURE 3.

Intermediate its ends the interior of the chimney is of reduced cross-section at zone 26 to increase the velocity of hot combustion gases flowing upwardly through the chimney from the burner. The zone 26 is cylindrical and the hot gases enter the zone 26 by way of a tapering frusto-conical portion 27 and leave it by way of a flaring frusto-conical portion 28 which opens upwardly into a cylindrical portion 29 merging with an outlet portion 30 from which the radial slots 6 extend.

Mounted in the top of the chimney is an aluminum well 31 of circular cross-section and provided around its upper edge with a radial flange 32 the underside of which rests on the top surface of the chimney 4. The underside of the clamping collar 8 is formed with a recessed portion around its annulus to receive the radialflange 32 of the well. The top surface of the chimney 4 is likewise recessed at 36 to receive and centre the flange 32 and therefore the well 31 correctly with respect to the chimney. The undersurfaces of the flange 32 and the peripheral portion of the collar 8 are machined flat as are the top surfaces of the chimney 4 on which they seat so that there is good thermal conduction between the top of the chimney and the collar 8 and flange 32. As is clearly shown in FIGURE 3 the annulus of the collar 8 tapers inwardly slightly towards its lower edge which registers exactly with the bore of the well 31. The marginal portion of the filter paper disc 10 is trapped between the top surface of the flange 32 and the collar 8 and the inside rims of the collar and flange which contact the filter paper 10 provide a hot boundary of circular shape.

The ring oven is assembled and used as follows.

The gas entry 3 is connected to a gas tap and the chimney 4 is rested on the base 1 around the hub 21. The flanged well 31 is then placed in the top of the chimney so that its flange 32 rests in the recessed portion 36 and the filter paper disc 10 is then placed across the top of the well 31 so that its marginal portion rests on the well flange 32. The clamping collar S is then placed over the top of the flange 32 thus sandwiching the marginal portion of the filter paper between the opposed surfaces of the ring 8 and flange 32. The glass shield 7, if required, is placed on the chimney flange 5 and the gripping piece 13 is mounted on top of the post 12 and is so adjusted that the lower end of the held pipette 14 containing solvent overlies the spot from which the ring is to be formed and which has been centered in the annulus of the clamping collar 8.

After assembly of the ring oven, the gas supply is adjusted and the burner 22 is ignited by way of an ignition and observation port 39 formed in the lower sidewall of the chimney 4. The combustion gases from the burner flow upwardly through the restricted portion 26 where their velocity is increased so that they impinge on the domed underside of the aluminum well 31 and are deflected thereby outwardly and upwardly through the cylindrical portion 29 to the radial gas outlet slots 6. The glass shield 7 prevents contamination of the filter paper 10 by the products of combustion which in drafty situations might be blown back over the top of the ring oven. Heat from the combustion products is transferred through the Wall of the well 31 to its interior and also by way of the top of the chimney 4 to the flange 32 and the clamping collar 8. As a result, the collar and flange are heated to a uniform steady temperature measnrable by a thermometer in hole 15, and, by adjustment of the gas supply to the burner 22, this temperature can be set to provide suflicient heat at the hot boundary to evaporate solvent before it has spread outwardly through the filter paper to the metal surfaces of the flange 32 and collar 8.

When the temperature of the upper portion of the ring oven has stablised solvent is allowed to discharge gradually from, the pipette 14 onto the spot 11. The solvent spreads outwardly through the spotted filter paper and is gradually heated by the heat trapped in the well 31. As the solvent approaches the hot boundary formed by the inside rims of the well and collar 8, it is heated relatively rapidly and is vaporized just before it reaches the metal surfaces of the collar and flange. Thus, the

constituents of the spot dissolved in the solvent are deposited at the hot boundary and form a thin ring in which the constituents of the sample are substantially uniformly distributed and are in substantially the same proportions as they occurred in the original sample spotted on the sheet 10.

When the sample has been transferred to the ring the pipette 14 is removed and a short period is allowed to elapse to dry the filter paper 10. As evaporation continues to occur at the hot boundary first, the solvent remaining in the filter paper continues to flow radially outwards so that no back migration of the constituents of the ring occurs.

When the filter paper is dry the gas supply is turned off and, after removal of the clamping collar 8, the filter paper can be removed from the oven. The ring may then be cut out and subdivided into a number of segments which can then be individually tested to determine the constituents of the original sample.

FIGURES 4 and 5 show the ring oven modified to enable a sample in the form of a spot or Streak, which may have been produced by a chromatographic run, to be concentrated. As rnany of the parts shown are identical to those already described they have been similarly referenced and are not again described.

It will be seen from FIGURES 4 and 5 that the ring oven has been modified by transferring the pipette gripping piece 13 to the top of a second post 40 which is attached at its lower end to the rear end of a strip holder 56 mounted on top of the post 12. The pipette gripping piece 13 is so adjusted that the lower end of the pipette can drip solvent onto the upper portion 43 of a strip of filter paper 44 on which the sample spot or Streak diagrammatically represented at 45, occurs.

Beneath the spot 45 the filter paper is cut with a narrow waist 46 which terminates at its lower end in a wider portion of the filter paper projecting downwardly into a slot 47 formed between two insert pieces 48 mounted inside the well.

The insert pieces are shown in more detail in FIG- URE 5. It will be seen that each comprises a solid block of aluminum having a part cylindrical outer surface 50 formed at its top end with a bead 51. Each insert 48 is provided along one edge with a projecting part 52 which provides with its inside face one end wall of the slot 47 and with its outside face a continuation of the part-cylindrical surface of the block. When the two inserts are placed together, as shown in FIGURE 5, they fit snugly inside the cavity of the well 31 so that heat transferred through the wall of the wall is transmitted through the inserts 48 to the slot 47. The bead 51 fits beneath the inside rim of the collar 8.

The strip 44 is held in position by having the top of its upper end-portion 43 trapped between a pair of glass slides 54, 55. The two slides are rectangular and the lower slide 54 is wider than the upper slide 55 to expose the uppersurface of the portion 43 of the strip 44 directly beneath the lower end of the pipette 14. The two slides 54, 55 are supported on a strip-holder 56 provided with a ramp surface 29 which slopes downwardly towards the axis of the well. At the lower end of the ramp surface the stripholder 56 is provided With -a pair of upwardly directed, spaced fingers 57 having a rebate formed between them so that the upper portion of the filter paper hangs down from the lower edge of the glass slide 54 and does not contact the strip-holder 56.

In the modification shown in FIGURES 4 and 5 sol- 'vent is discharged gradually from the lower end of the pipette 14 onto the upper portion 43 of the strip 44 exposed beneath the narrower slide 55. The solvent spreads downwardly through the strip 44 and past the sample spot 45. Constituents of the sample dissolve in the solvent and are carried downwardly with the solvent towards the waist 46. As a result of the progressive reduction in cross-section of the strip 44 the concentration of sample dissolved in the solvent is increased. At the lower end of the waisted portion 46, the strip enters the slot 47 and is maintained by heat radiated from the sides of the slot at an elevated temperature determinable by a thermometer 60 in hole 15. As a result the solvent vaporizes along a line extending through the waisted portion 46 immediately above the slot 47. The constituents of the sample therefore are deposited along this line and when all of the sample has been transferred from the spot to the solvent vaporization line the discharge of solvent from the pipette is discontinued. The remaining solvent in the strip 44 continues to flow downwardly towards the waisted portion where vaporization takes place. Within a relatively short period of time the waisted portion of the strip 44 is dried and the section containing the sample may then be cut out and used for further analysis or for expanding the sample by means of the ring oven technique described with reference to FIGURES 1 to 3.

From the above description it will be appreciated that the ring oven devised by the applicant is more Versatile than conventional ring ovens in that it ena'bles concentration by means of waisted strips as well as concentration by Conventional ring oven techniques to be used. Also, it is less expensive than the Conventional ring oven as there is no complex electrical control unit, no element to burn out or -be water-shorted or acid corroded. Additionally, adjustment of the temperature of the ring oven is readily controlled by means of a gas tap and the time taken to heat the ring oven to its stable temperature is reduced as compared with a Conventional ring oven. Further, the component parts such as the chimney, clamping collar and well are all made of the same metal, preferably aluminum, and can 'be easily dismantled for cleaning and then fitted together. Further the thermal capacity of the chimney is considerably greater than the thermal capacity of an electrically heated ring oven block so that the temperature stability of the ring oven described is superior.

It is to be understood that although the described hot boundary is provided by a metal rim, in some cases, such as when elution of the spot is to be carried out by hydrochloric acid solution, a heat conductive material other than metal and inert to hydrochloric acid may be used. Such a material may for example comprise glass or ceramic.

I claim:

1. A ring oven comprising:

(a) a base,

(b) gas burner means on said base,

(c) chimney means resting on said base and surrounding said gas burner means,

(d) heat-conducting well means mounted on said chimney means, said well means closing the upper end of said chimney means and extending downwardly therein to define therewith an annular passage,

(e) gas outlet means extending through said chimney means from said annular passage,

(f) an annular filter paper support surface at the upper end of said well means,

(g) annular clamping means for holding filter paper on said support surface to span said well means, the inside diameter of the clamping means being the same as the inside diameter of said support surface,

(h) means for locating said clamping means coaXially of said support surface,

(i) pipette support means, and

(j) a pipette carried by said support means with its lower end overlying the center of said annular support surface.

2. A ring oven as set forth in claim 1, in which the chimney means is formed between the well means and the burner means with a portion of reduced cross-section.

3. A ring oven as set forth in claim 1, in which the chimney means has an opening adjacent the said burner means and a recess in its top surface, a radial top fiange 7 on the said well means partly seating in said recess, said locating means comprising a rim on said clamping means engaging over said flange on said well means.

4. A ring oven comprising: (a) abase, (b) a gas inlet projecting radially outwards of said base, (c) a hub formed centrally on the top surface of said base, (d) a 'burner projecting upwards from the centre of said hub and communicating with said gas inlet, (e) a chimney resting on said base around said hub, (f) a restriction formed intermediate the ends of said chimney, (g) lateral gas outlets at the top of said chimney, (h) a heat-conductive removable well of circular crosssection mounted inside the top of said chimney, (i) a radial flange on said well resting on the top of said chimney, (j) metal inserts fitting snugly inside said well and defining between them an upwardly opening slot, (k) support means extending upwards from the top of said chimney, (l) strip-holding means detachably mounted on said support means, (In) pipette-holding means detachably mounted on said support means above said strip-holding means, and

(n) a pipette held by said pipette-holding means to be positioned above waisted strip means hanging from said strip-holding means into said slot means.

5. A ring oven as set forth in claim 4, in which said support means comprises a first post fixed in the top of the chimney, a slide carrier having an inclined slide supporting surface and detachably connected to the top of said first post, a second post of the same cross-section as the first post and extending upwardly from said slide carrier, the pipette-holding means being detachably mounted on the top of the second post.

6. A ring oven as set forth in claim 4, including a removable draft shield resting on top of the chimney.

7. A ring oven as set forth in claim 4, in which said chimney, said well and said flange are made of aluminum.

References Cited Weisz, H., Microanalysis by the Ring Oven T echnique, Pergamon Press, New York 1961, pages 15-17 and 31 relied on.

Millipore Filter Corporation, Application Data Manual ADM-70, 1963, pages 24 to 26 relied on.

MORRIS O. WOLK, Primary Exam'ner.

R. M. REESE, Assistant Examiner.

U.S. C'l. X.R. 

